**5. Data processing and mapping method**

The raw data, including BSSS mapping data, HOV attitude data, acoustic positioning data, sound velocity data, are processed in two steps (pre-processing and post-processing) to obtain topographical and geomorphology map. Data pre-processing mostly consists of five steps: navigation data processing, rewriting navigation data, coarse error elimination, angular deviation correction, and port/ starboard position correction. Data post-processing mostly consists of 12 steps, namely installation angle correction, sound velocity correction, attitude data filtering, bathymetric data filtering, fine error elimination, field correction, side-scan data filtering, bottom tracking, angle variation gain, equalization gain, data export, and mapping. **Figure 12** shows the flow diagram of data processing and mapping.

#### **5.1 Data pre-processing**

1.Navigation data processing

Post-process navigation and acoustic positioning data, such as FOC, DVL, USBL, and LBL, to obtain high-precision navigation data.

2.Rewriting navigation data

Rewrite high-precision navigation data to the BSSS raw data file to replace original navigation data.
